In a bid to reduce the amount of diesel consumed by haulage trucks in the open cast mining sector, local engineering company Siemens South Africa (SA) has launched its latest generation 11 MW fully automated direct current (DC) containerised substation – the Siemens E-House, Chantelle Kotze writes.

Unveiled at the company’s head office in North Riding, Johannesburg, in September, the containerised substation with trolley assist technology is used in the mining industry to overcome the limitations of haulage truck engine power when moving uphill or on ramps. The trolley assist solution is installed on any uphill stretch between the pit and off -loading points to assist with hauling, as the speed on the gradient is limited by the diesel engine’s horsepower, explains Siemens SA project manager Phiwa Thindwa.

The substation provides electric power to overhead DC power lines, which in turn provides the DC power to adapted diesel-electric haulage trucks, providing the trucks with much needed power on uphill haul segments within the mine. With the inclusion of the electric drives, the electric power supplied to the wheel motors of the haulage trucks also enables the trucks to move faster uphill. This results in quicker turnaround times and higher productivity for the mining operation.

Thindwa explains that the haulage trucks run on diesel power in the pit and around the crusher, then switch to electric power when moving uphill. “The move to electric power on an uphill significantly reduces diesel consumption when travelling uphill, which can account for up to 80% of a mine’s diesel consumption,” he highlights.

Moreover, using trolley assist on gradients reduces the cycle time of the haulage trucks, thus increasing intervals for maintenance. This leads to longer intervals between engine overhauls, which are proportional to the hours that the haulage truck is in operation, and resultantly reduces downtime, in turn improving productivity.

Each 11 MW fourth generation containerised substation – the largest unit ever manufactured by Siemens SA – has 1.8 kV of DC voltage and up to 10 000 Amps, with the capacity to simultaneously run two 300 t trucks continuously, three trucks for 10 minutes or four trucks for one minute.

As the only provider of the trolley assist solution in the Siemens group, Siemens SA embarked on the development of the fourth generation E-House units when it was awarded a bid to provide electric power to adapted diesel-electric haul trucks for a uranium mine in Namibia last year. Siemens SA has completed three of the six 11 MW substations destined for the mine to date. The first three were shipped to site in September, with the remaining three to be delivered in the coming months.

Siemens SA lead engineer Karl van Rensburg, who designed the substation, says they will be used to power a fleet of Komatsu 960E trucks, which are among the industry’s biggest and highest capacity mine haulage vehicles, with a load capacity of 214 m3 or 327 t.

He points out that 90% of components in the containerised substations are entirely manufactured by Siemens, compared to earlier generation units that contained approximately 30% Siemens components. With components currently imported from Germany, each Siemens substation is assembled in Pretoria and housed in a 6 m x 3.3 m x 3 m container that weighs approximately 8.5 t when fully commissioned.

The container includes the 1.8 kV DC switchgear, rectifiers, 33 kV ring main unit, Siprotec AC protection device and Sitras Pro DC Feeder protection device. The entire substation is automated with a Siemens PLC, connected via Profibus, and controlled via a touch panel.

Given the success of the solutions in the mining sector, SA country business unit leader for rail electrification Joey Govindasamy notes that Siemens will be targeting rail customers in the near future.